| Rising atmospheric carbon dioxide concentration [CO2] is a major driving factor for global warming, meanwhile it increases crop production as photosynthesis substrate. Rice is one of the most important food crops in the world. Although a number of studies reported that elevated [CO2] had beneficial effects on rice growth and grain yield, it is still unclear whether the fertilizer effect of CO2occurs to all rice cultivars. In order to select or breed rice genotypes with better adaptation in future environment, it is very necessary to study the genotypic variation in rice response to elevated [CO2] and to elucidate the associated mechanisms, especially under fully open field conditions.This research was designed to study the influence of elevated [CO2] on phenology, plant height, tillering dynamics, dry matter accumulation and allocation as well as yield and yield components of12rice cultivars, which are Wuyunjing21, Yangfujing8, Wuxiangjingl4, Wujingl5, Ⅱyou084, Shanyou63, Liangyoupeijiu, Yangliangyou6, Zhenshan96, Yangdao6, Yangfuxian6and Yangdao8. An FACE (Free Air gas Concentration Enrichment) experiment was conducted in a rice field at Xiaoji town, Jiangdu County, Jiangsu Province, China (119°42’0"E,32°35’5"N) using unique FACE system in the world. Rice plants were grown at ambient or elevated [CO2](200μmol mol-1above ambient) for entire growth period.The results showed that:1. Averaged across all tested cultivars, elevated [CO2] significantly accelerated phenology development of rice before heading, with growth duration from sowing to heading showed1day less for plants grown under FACE conditions, however, different cultivar responded differently to elevated [CO2] in terms of magnitude or even direction. The phenology development after heading was not affected by CO2enrichment, similar trends were observed for all tested cultivars.Elevated [CO2] significantly increased plant height at jointing stage, heading stage and maturity by2.8%,3.2%and2.9%, respectively; similar trends were observed for all tested cultivars.Elevated [CO2] significantly increased tiller number of all rice cultivars at tillering stage, jointing stage, heading stage and maturity by15.2%,13.5%,12.1%and12.7%, respectively; Significant interactions between CO2and cultivar were detected at maturity stage. Productive tiller ratio was slightly reduced by elevated [CO2], similar trends were observed for all tested cultivars.Elevated [CO2] significantly increased dry matter accumulation at tillering stage, jointing stage, heading stage and maturity by15.2%,20.4%,19.3%and18.4%, respectively; Significant interactions between CO2and cultivar were only detected at heading stage.2. The biomass accumulated from transplanting to jointing stage, jointing to heading stage and heading to maturity was significantly increased under FACE by18.4%,20.6%and16.9%, respectively. There was no significant interaction between CO2and cultivar with respect to the biomass accumulated during each growth stage of rice.3. Assimilate allocation of rice plants were changed by elevated [CO2]. Elevated [CO2] significantly decreased the ratio of green-leaves dry weight to total dry weight of plant at tillering stage and heading stage by5.7%and8.9%, respectively. The ratio of sheath dry weight to total dry weight of plant was increased significantly under FACE conditions by3.5%and3.6%at tillering stage and heading stage, respectively. The ratio of root dry weight to total dry weight of plant was significantly increased under FACE conditions by7.8%and9.6%, respectively. The ratio of panicle dry weight to total dry weight of plant and harvest index were not affected by elevated [CO2]. No significant interaction between CO2and cultivar was detected for all above parameters.4. Elevated [CO2] significantly increased panicle number per unit area and spikelet number per unit area by14.3%and14.7%, respectively. No significant CO2effect was found for other yield components such as spikelet number per panicle, filled grain percentage and1000-grain weight. Significant interactions between cultivar and CO2were detected for panicle number per unit area and spikelet number per panicle, while no interaction was found for other yield components.5. Grain yield of all tested cultivars in FACE plots were significantly higher than ambient plots by125g m-2, which equals to14.7%increase in average. ANOVA results revealed significant interaction between CO2and cultivar for grain yield, hybrid rice cultivars (20.8%) showed greater response to elevated [CO2] than conventional indica (13.0%) or japonica (8.6%) cultivars.The above results indicated that the yield improvement of rice under elevated CO2concentration was partially related to the increase of panicle number per unit area and spikelet number per unit area from the aspect of yield components. The positive yield response of rice to high CO2concentration was also closely associated with larger biomass production under FACE conditions, while the proportion of assimilates allocated to grain contributed little to yield promotion. |
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